The present invention relates to a device for damping the shocks caused by heavy objects and particularly as a result of the accidental dropping of transported packages into ponds for the discharge of radioactive products. These packages, which are also called coffins or flasks, will be termed caskets throughout the remainder of the description.
As it is never possible to completely exclude an operating fault in manipulating devices, it is necessary to take action against risks of the fracture or unsatisfactory operation of the casket attachment system at the time when the casket is located above the discharge pond and during its descent to the bottom of said pond.
A break or fracture to the system would lead to the casket dropping and during its impact with the pond wall would on the one hand make a hole in the wall and on the other, if the casket was very heavy, could break through the concrete floor on which the wall is located and cause unacceptable damage to adjacent structures.
Various solutions have already been proposed for obviating this risk of damage. For example an attempt has been made to place a cellular concrete layer between the bottom of the pond and the concrete floor. However, to obtain an effective action, the layer must be very thick (several meters in the case of a casket weighing approximately 120 tons). In addition, it is necessary to monitor the sealing of the pond, because cellular concrete is very sensitive to the action of water. Thus, the layer could form a contamination trap.
Another known solution consists of placing on the bottom of the pond tight metal shock absorbers having a honeycomb structure and whose cavities are filled with air. These cushioning layers are effective, but onerous. It may also be necessary to ballast or fix the cushioning layers to the bottom of the pond and insure their sealing. The reason is that, when filled with water, said layers are ineffective. Furthermore, such cushioning layers are only effective if they receive a vertical impact force and not an oblique impact force.
It has also been proposed to vertically arrange at the bottom of the pool water-filled, perforated tubes. These tubes do not deform in a homogenous manner and are subject to a counterpressure at the time of the impact produced on the one hand by a relatively slow escape of the water through the tube orifices and on the other to the incompressibility of the water contained in the tube.